Question

Electron affinity is positive for the case when :

• A. $O$ changes to $O^{-}$
• B. $O^{-}$ changes to $O^{2-}$
• C. $O$ changes to $O^{+}$
• D. none of the above

Answer 1

The correct option is B $O^{-}$ changes to $O^{2-}$

Electron affinity is the energy released when an atom accepts an electron. However, due to electron repulsion, when $O^{-}$ accepts an electron and changes to $O^{2-}$, electron affinity becomes positive. The incoming electron in $O^{-}$ faces repulsion and hence, its acceptance is disfavoured.